This invention relates to a prosthetic acetabular cup inserter which is particularly, although not exclusively, applicable for minimally invasive surgery (MIS) with small incisions. The inserter can also be used to orient the cup outer shell in the acetabulum and to impact it. The outer shell generally receives a polyethylene or ceramic bearing which in turn receives the spherical head of a femoral component. The invention allows the inserter to have a curved shape although the invention can be applied to inserters with a substantially axially straight shape.
WO 2004/010882 shows a surgical impactor which is intended for engagement with a threaded implant. The cup holder is provided with a collet which carries a screw thread and the collet can be opened or closed by operation of a tapered cam. The cam is resiliently biased into its operative position to open the collet to collapse which reduces or collapses a screw thread to detach the impactor from the implant.
A fundamental problem with this construction is that the cam is not forceably held in its operative position but merely relies upon a spring so that the cam can move backwards against the spring in certain circumstances thus reducing the grip on the implant. Moreover, the available area of the collet for engaging the implant is restricted by the cover which must extend over the collet to locate it in place.
Curved acetabular cup impactors/inserters/reamers are shown in U.S. Patent Publications 2003/0050645, 2003/0229356 and 2004/0153063.
Straight impactors showing devices for gripping the outer shell of the acetabular cup system are shown in U.S. Pat. Nos. 4,632,111, 5,169,399, 5,571,111, 5,540,697 and 5,954,727.
U.S. Pat. No. 4,632,111 shows apparatus for positioning a prosthetic acetabular cup within an acetabulum and relies upon an expandable elastomeric annular collar. The collar is expanded by operation of a hand retainer nut which acts on a threaded stem to provide pressure against the annular collar so that it can be compressed and its diameter increased to grip the inner surface of the cup to be implanted.
It would be very difficult to use this device where there is little available room for the surgeon to operate, especially for minimally invasive surgery (MIS) with a short incision. The present invention is intended to overcome the difficulties of both the above earlier disclosures and to provide a prosthetic acetabular cup inserter which is easier to operate.
As used herein, when referring to bones or other parts of the body, the term “proximal” means closer to the heart and the term “distal” means more distant from the heart. The term “inferior” means toward the feet and the term “superior” means towards the head. The term “anterior” means towards the front part of the body or the face and the term “posterior” means towards the back of the body. The term “medial” means toward the midline of the body and the term “lateral” means away from the midline of the body.